Prosthetic heart valves can be used to treat cardiac valvular disorders. The native heart valves (the aortic, pulmonary, tricuspid and mitral valves) serve critical functions in assuring the forward flow of an adequate supply of blood through the cardiovascular system. These heart valves can be rendered less effective by congenital, inflammatory, or infectious conditions. Such conditions can eventually lead to serious cardiovascular compromise or death. For many years the definitive treatment for such disorders was the surgical repair or replacement of the valve during open heart surgery.
A transcatheter technique can also be used for introducing and implanting a prosthetic heart valve using a flexible catheter in a manner that is less invasive than open heart surgery. In this technique, a prosthetic valve can be mounted in a crimped state on the end portion of a flexible catheter and advanced through a blood vessel of the patient until the valve reaches the implantation site. The valve at the catheter tip can then be expanded to its functional size at the site of the defective native valve, such as by inflating a balloon on which the valve is mounted. Alternatively, the valve can have a resilient, self-expanding stent or frame that expands the valve to its functional size when it is advanced from a delivery sheath at the distal end of the catheter.
Transcatheter heart valves (THVs) may be appropriately sized to be placed inside most native aortic valves. However, with larger native valves, blood vessels, and grafts, aortic transcatheter valves might be too small to secure into the larger implantation or deployment site. In this case, the transcatheter valve may not be large enough to sufficiently expand inside the native valve or other implantation or deployment site to be secured in place.
Replacing the pulmonary valve, which is sometimes referred to as the pulmonic valve, presents significant challenges. The geometry of the pulmonary artery can vary greatly from patient to patient. Typically, the pulmonary artery outflow tract after corrective surgery is too wide for effective placement of a prosthetic heart valve.